Optical crown glasses



June 24, 1969 H. ,BROMER ETAL 3,451,829

OPTICAL CROWN GLASSES Filed April 12, 1966 4O 5O 60 7O 8O "FD "cl INVENTORS.

HEINZ BROMER NORBERT MEINEPT I BY 0% 1J6? ATTORNEYS.

United States Patent 3,451,829 OPTICAL CROWN GLASSES Heinz Bromer, Kreis Wetzlar, and Norbert Meinert, Wetzlar, Germany, assignors to Ernst Leitz, G.m.b.H., Wetzlar (Lahn), Germany 3,4'5 Patented June 24, 1969 ing to another definition, has a higher v -value than the normal glass. The dilference of the v -value is customarily designated Av -value. According to the definition for the s'g (plus) glasses the Av -value will be positive, and given in units of the v -values for .9'g(minus) glasses Filed Apr- 12, 19 SEE 542,035 will be correspondingly negative. Claims P y, application y, P 29, 1965, 'In the accompanying drawing two glasses are desig- 50,618 0 nated schematically in a Sg-v -diagram. Therein accord- US Cl 106-47 (303 3/3 2 Claims ing to the definition given above, glass 1 is indicated as S'g(plus) wlth a Av -value of +10.4 and glass 2 is a s'g(minus)-glass with a Av -value of -9.6.

It would now be found that one can obtain very stable ABSTRACT OF THE DISCLOSURE crown glasses with positive deviation, +Av if one uses Optical CI'OWII glasses with anomalous Partial p for glass formation metaand orth-phosphates of alumisions are presented. Said glasses are prepared fr m num as well as alkaline earth phosphates. The portion of miXeS Consisting of aluminum P phates from 45-55% phosphates of aluminum lies between 45% by weight by weight, alkaline earth phosphates from 510% by and 55% by weight. The portion of alkaline earth phosby weight, alkali oxides from 1020% by weight, a aphate amounts to from 5% by weight to 10% by weight. line earth oxides, Zn, Cd from 15-30% by Weight a d In order to obtain the highest possible Av -value it is up to 10% by weight of TiO effective to add up to 10% by weight of titanium dioxide,

TiO

It is advantageous, to use alkali oxide together with The subject matter of our invention are optical crown the titanium dioxide i an mo nt fro 10% b i ht glasses with anomalous partial dispersions. to 20% by weight of alkali oxides in order to obtain the -It has long been known that a correction f th C I dclearest possible glasses. The alkali oxides serve moreary spectrum of objectives is possible only when at least over for the control of the middle indices of refraction one of the glasses used for this purpose exhibits an 3 0- n of the glasses. For adjustment of specific optical values malous partial dispersion value it is moreover advantageous to add oxides of Mg, Ca, Sr, Ba as well as Zn and 0d. The amount of these oxides should lie between 15% by weight and 30% by weight. In known manner small amounts of decolorizers, for example, arsenic trioxide, may be added. d'g=,, Examples of glass mixes according to the invention nF no are given in the following tables.

In the section designated Av is given the deviation of the v values from the curve for normal glasses in the All so-called normal glasses exhibit a partial disper- 3g ve dlagram' TABLE 1 sion .s'g which over a wide range is in approximately Composition. Percent by Weight linear dependence from the mean dlsperslon val V 40 A1(p03)3 390 This means that all of these glasses lie in a Straight line (p 7 1 in a diagram whose abscissa indicate the Ve val e a AIPQ1 0 whose ordinates indicates the s'g value. This holds in K20 155 each case for a v value which is greater than 35. Cao 4'0 With v -values which are smaller than 35, the Sg-V g 9 4 rises more steeply than would correspond to linearity. In Zno the usual diagrams, in which the middle index f r fr o 33 tion n is established on the ordinate, these glasses will be designated as heavy flint. These heavy flint glasses A mlxefl chafge 0f aboflt Introduced posses accordingly a stronger dispersion in the blue resuccesslve portions into a platinum crucible, finally held gion of the spectrum than other glasses. In other words, for 120 mlmltes at 1350' C', the}! Stlrred p the B'g-values exhibit deviation to high values as comlure 1050 wlthollt Stlmng, permlttfid to pal-ed to normal values so that these glasses are d i crease 1n temperature to 950 C. and then cast 1n carbon nated as 3g (plus) glasses. Reversely, the glasses whose molds- .S'g-value is less than the normal glasses are designated The Values are: as S'g (minus) glasses. Physically this means that their 15 0 dispersion in the blue region of the spectrum is smaller 719:52'63 than that of the normal glasses. If one compares, however, a glass with normal disper- AVa: +7 9 sion with a glass with anomalous partial dispersion, 60 whose Sg-values are equal, they exhibit a variation in The given optical data are measured values of a comtheir mid dispersion value v A ,s'g (plus)-glass, accordpletely annealed glass.

Melt No. Ca(POa)2 A (POa)3 AIPO4 K20 CaO BaO ZnO T102 N 820 he a 19E(X10-) AV 7.1 49.0 13.0 3.4 9.3 13.4 2.8 2.0 1.5690 51.8 5041 +7.4 7.1 49.0 2.0 14.7 3.4 9.3 11.7 2.8 1. 5642 51 .9 5014 +5.6 7.1 44.0 5.0 16.7 3.4 9.3 11.7 2.8 1 .7 5028 +7.3 7.1 39.0 10.0 16.7 3.2 11. 7 2 .g gag: if? iIi 2&8 ii?) i212 210 9:4 717 313 5038 +7.9

3 Having described our invention, we claim: 1. Optical crown glass with anomalous partial disperion 1 ix- F :haracterized in that it is prepared from a mix which :onsists of aluminum phosphates from 45 to 55 percent 3y weight, of which up to about 14% may be A1PO and the balance Al(PO alkaline earth phosphates from 5 to 10 percent by weight as glass formers, alkali )xides from 10 to 20 percent by weight and oxides of Mg, Ca, Sr, Ba, Zn, Cd from 15 to 30- percent by Weight.

2. Optical crown glass according to claim 1 characterized in that it contains up to 10 percent by weight 15 4 References Cited UNITED STATES PATENTS TOBIAS E. LEVOW, Primary Examiner.

0 I. COOPER, Assistant Examiner.

US. Cl. X.R. 

